Questions tagged [rf]
Short for Radio Frequency, i.e. frequencies at which radiation (intentional or not) plays a role. Typically associated with wireless communications, but also relevant for high-speed PCB design.
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Send wireless signal from a wireless relay to turn a wireless lamp on
I have this wireless relay:
The receiver is connected to a pump which is on the 1st floor of our house and can be controlled from the 3rd floor of our house. We have a neighbor (my sister) who can ...
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I need help understanding the envelope detector part
I started reading "Build Your Own Transistor Radios" by Ronald Quan and I don't get how the envelope detector works in his TRF radio.
I know that a "classic" envelope detector ...
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MOSFET ring oscillator LT SPICE
I am designing a ring oscillator using MOSFETS to create the inverters however, I am encountering problems with the output. I feel like the ring oscillator project should be very simple and yet I can'...
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How likely can a Bluetooth IC get damaged if the antenna has a wide bandwidth?
I design a device with a Bluetooth low energy chip (DA14863) that sits at different positions on the human body (minimal distance of 0.7mm). Simulation shows that the human body absorbes up to 95% of ...
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Equivalent traditional transmission line of another with lossy return path [closed]
Take the typical lossy transmission line below. As with most textbooks, it is simply stated that R represents the loss on a conductor including the skin effect, and L is the inductance of the line, ...
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sr-t500 walkie-talkie module [closed]
I have the sr-t500 walkie-talkie module.
Everything works fine, but the sound is not sent through the microphone!
I tried replacing the microphone, but there was no change.
Does anyone have ideas ...
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How do you chain 2-port S-parameters onto a 1-port S-parameter?
With 2-port S-parameters, you can build up a circuit by chaining them together using ABCD or T-parameters, simply multiply the matrices:
We have measured a complex single port S-parameter of an ...
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PE44820 Phase Shifter Confusion in Results
I am using a PE44820 phase shifter for my capstone project. We created our own evaluation board so that we can test it with a raspberry pi3. We are running a simple test first where we are just trying ...
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Why does this Gilbert cell configuration not have good local oscillator suppression?
I'm doing some simulations in ADS of a Gilbert mixer based on BJTs:
If I connect the base of transistor X6 directly to GND for the AC signal like in the picture above, the mixer has a very strange LO ...
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Is it theoretically possible to make an anti-jammer for WiFi? [closed]
From the little I understand of WiFi jamming, it uses strong counterfeit signals that overwhelm legitimate signals.
I thought perhaps a device that emitted the same frequency but offset so that it ...
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Does the law of reciprocity hold true for the phase response of an antenna?
I know that an antennas spectral transfer function should be the same in both transmit and receive due to the law of reciprocity, however does this law hold true for the phase response (AKA phase ...
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How to design 433 MHz RF with SYN470R?
In this document, I see that 50 Ω of the antenna is mentioned, but what makes me wonder is that in the table below, each strange frequency has a separate impedance, Zin.
What is Zin and what does it ...
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How to make an 802.11b/g conducted power measurement, getting different results
I am an engineering co-op tasked with measuring the output power of an avionics WiFi unit. I want to measure the maximum conducted power at the coax port to then calculate max EIRP.
The challenge is ...
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Balanced vs differential signals
I would like to verify my understanding of the following scenario with regards to why coax is 'unbalanced' and how a choke interacts with this unbalance:
Consider a half-wave resonant dipole, if one ...
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low power rf ring oscillator transistors
I am trying to design a ring oscillator with RF transistors and was confused about the transistors that should be used. I have not found an explicit answer online - if you know of a resource I missed ...
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NFC antenna design - moving from rectangular to circular
I'm working on a design using an NXP PN7150 NFC chip with PCB antenna. My initial prototype used their online tool for the antenna design, to generate the values for the matching network, however this ...
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Fixing SMB adjustable contact to its SMB connector (Jack)
I recently purchased an SMB adjustable square flange jack connector: R114413000 [Partlink].
In the bag, I receive the adjustable contact and the connector:
How do I fix this adjustable contact to the ...
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Impedance adaptation for two frequencies
I just received my first custom RF board that use 2.4 GHz and 5 GHz with a diplexer.
Unfortunately, it appears that the used PCB stack-up wasn't really what I expected so my traces are not 50 Ω, but ...
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Matching network for a radio
I’m trying to understand how the matching network functions on the radio side of a transmission line. As an example, here’s an excerpt from the Nordic nRF52840 DK schematics.
As I understand it, when ...
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Demodulation of FM signal frequency
After playing with homemade AM radios, I noticed that it is boring to broadcast AM signals all alone. I have also noticed that the AM stations around us, are so limited that I had no other chance than ...
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3 dB Power Divider Used as Power Combiner S Matrix Explanation
I'm trying to understand the operation of an ideal RF power combiner.
Below is the scattering matrix of such device. (i.e. Wilkinson Power Divider)
\$[S] = {\frac {-j}{\sqrt {2}}}{\begin{bmatrix} 0 &...
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High power, wideband balun transformer
I wish to design a 'somewhat'(ill-defined; i take what i can get) compact balun connected from a coax cable to a custom design dipole antenna. The design of the antenna is wideband in the sub 1 GHz ...
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Review of PCB RF Design
I designed a 4 layer RF board with the NRF24L01+. When I got the boards in to test I was not able to establish a radio link with some other NRF24L01+ modules. I have attached my schematic and board ...
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Attenuation only at transmit without affecting receiver
My office in a basement and I have bought an amplifier in AliExpress to be able to make calls from the basement.
The local cellular company says my amplifier is blocking close by cells (oops). Is ...
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Impact of rain fade on 60 GHz radio links
I'm a junior network admin at an ISP and need your help regarding point-to-point links with devices using the 60 GHz band.
PROBLEM
Most of them, except the ones that are at very close proximity (e.g., ...
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AM radio spectations - how does it work
I have captured a RF-AM transmitter circuit on internet. It is clear that the input signal will be pre-amplified and then it will begin to modulate the signal. The question is about how the circuit ...
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Frequency detector/comparator problem
I have recently learned about schmitt and comparator op amps, and I came up with an idea to build a "frequency comparator" (if it is called like this). The function of this circuit is to ...
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Why do amplifiers have minimum frequencies?
RF amplifiers, both power amplifiers and low noise amplifiers, are rated with a minimum and maximum frequency. For example, the Analog Devices HMC517LC4 Low Noise Amplifier has a frequency range of ...
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Understanding Parameters of Antennas
I would appreciate it if you could check my assumptions regarding the application of antennas in my design, which usually involve cellular and Wi-Fi technologies. Sometimes, I come across parameters ...
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Antenna tuning of 2.4GHz WiFi board
I am new to the RF electronics and tuning of antennas. I am working on a 2.4GHz Wi-Fi board design using an ESP32-S2 chip. The board consists of a 50 ohm single ended impedance trace for the antenna ...
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Implementing a light software stack on STM32 to send and receive data using 433Mhz RF modules
I need to send a 12-bit data continuously from one system to another using 433MHz RF modules. The transmitter and receiver systems uses STM controllers (STM32L010F4) which are connected to the radio ...
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Antenna polarization confusing
How do we mount an antenna which is a meandered line shape, to be in vertical or horizontal polarization? Vertical pol means that the antenna mounted to vertically to the earth. I’m confused just ...
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Can you calibrate your VNA to show matching circuit behavior, without the antenna connected?
We need to make a matching circuit for an antenna, but the antenna feed point is in an inconvenient location.
Is there a way to calibrate the VNA at the feed point such that the VNA will show the ...
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Parasitic inductance when probing high frequency signals with MMCX connectors?
I am using an oscilloscope to probe some high-frequency circuits (a SMPS). On my circuit board, I have installed some MMCX connectors to connect my probes to. These MMCX connectors have a short ...
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ISO permitted RF emission spectrum for medical devices in hospitals
I've been searching to find the electromagnetic compatibility requirements for medical devices to be used in hospital but cannot find the correct ISO standard. The list here only lists implantable ...
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Tricking CPU's with specially crafted RF signals
Is it possible that I can modulate and craft a RF signal that, once demodulated by a WiFi card and turned back into electrical signals or binary data, can trick the CPU into thinking it's a command ...
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What is the best practice when replacing a ribbon-cable ferrite clamp with chip ferrite beads?
I'm working on EMC testing a product. We have an internal 30 cm ribbon between 2 boards. One has a MCU and LCD, and the other MOSFETs and a 3 A switching regulator.
We determined that a lot of RF is ...
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FPC and PCB trace antennas difference
I see lots of PCB trace antennas in green color layer, as I know the dielectrics. On the other hand, there are FPC antennas (flexible printed circuit board antennas) are mostly in somehow black color, ...
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How can I convert a high frequency sine signal to a square wave?
I'm trying to convert a high frequency sine wave signal (approximately 130 MHz) with lets say 3 Vpp into a square wave signal (also 130 MHz) with 0V and 5Vp. The square wave is subsequently used as a ...
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Level shifting from 3.3 V to 1.8 V at 500 MHz
How can I translate a unidirectional signal from 3.3 V to 1.8 V with a bandwidth of 500 MHz?
The signal I am interested in is the output of a high speed comparator (TLV3601) and I have to measure the ...
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How should I approach the circuit analysis of this reflexive receiver? [closed]
I built the following circuit:
I got this circuit from this YouTube video.
It works well, although the volume is quite low. My main question is how would I approach circuit analysis of this circuit ...
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Skills to build an airborne radar [closed]
I am currently working on a project to develop an airborne ground penetrating radar - a payload to be put on a drone - we are aiming to develop a synthetic aperture ground penetrating radar of this ...
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Broadband Impedance Matching Simulation of Helical Antenna: Convergence to High-Low Zo Transitions
Hello esteemed colleagues,
I've embarked on a comprehensive study involving the simulation of broadband propagation of helical antenna impedances through a segmented transmission line (TL) impedance ...
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Output matching influences the input matching (RF amplifier)
Prerequisites
I try to design a radio frequency low noise amplifier with a SiGe transistor (BFP740 infineon.) The amplifier is designed as a common emmiter with inductive degeneration.
Observation
...
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RF output impedance on ESP8684 series
I'm looking for the output impedance on the RF pin of the ESP8684 SOCs.
On other application note like for the ESP32-C3 it mentioned that the output impendance of the RF pin is 35 + 10j.
But for the ...
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Where should the audio-input be available in this RF circuit?
Let me show you what I have tried so far. First of all, the circuit below has been tested and this one works for sure. The audio signal can be heard on an FM radio at 100MHz.
The second below is ...
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How are RF filters constructed?
I want to know what filter circuits look like in the RF (MHz-GHz) frequency range. Are they just like low frequency LC filters, but with appropriately adjusted component values?
For example the VLF-80+...
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Why grounding the circuit with external stuff, when a capacitor can do it?
I am examining my own radio circuit now for several days, so I included a pic:
When the circuit has been powered up, it works fine without fingers or equal grounding methods, for example by getting ...
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Two port antenna isolation effect
I wonder and imagine if one antenna systems having two ports for two different working frequencies (so two different antenna elements included inside of it), what is the port isolation importance in ...
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Can SP2T RF switches be considered failsafe?
I am looking for a RF switch that is failsafe.
For failsafe I mean:
a device that defaults to a useful state during total power loss (no supply voltage, no control voltage)
for a RF switch, a device ...
